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HomeMy WebLinkAboutPN_KennydaleLakeline_ProjectNarrative_180416_v1Technical Memorandum \\IWRS007FS1\Projects\01621\135-01621-16001\SupportDocs\Permitting\Kennydale Lakeline Summer 2018 Work TM. 03272018.docx 1420 Fifth Ave , Suite 600, Seattle, WA 98101P Tel 206 883 9300 Fax 206 883 9301 tetratech.com Date: March 28, 2018 To: David Christensen, City of Renton Cc: Lara Kammereck, Carollo Engineers Inc. Daniel Reisinger, Carollo Engineers Inc. Andrew Colby, Tetra Tech From: David Scott Project: Renton Kennydale Lake Line Condition Assessment Project Number: 135-01621-16001-02 Subject: Description of Proposed Summer 2018 Work Background In conjunction with the ongoing Kennydale Lake Line Condition Assessment, pipe condition assessment, manhole installation and pipe cleaning is proposed in Lake Washington during the 2018 summer fish window. In order to proceed with that work which includes excavation in the Lake permits will be required and a JARPA permit application will be submitted. This document provides background and a summary for the proposed work as well as information related to the attached permit figures. The proposed work follows the Phase 2A of the Lake Line Condition Assessment which included ultrasonic thickness (UT) testing and visual inspection of exposed portions of the lakeline as well as survey, bulkhead assessment and hydraulic assessment. As part of the hydraulic assessment it was concluded that the hydraulic capacity of the lake line is reduced, indicative of partial blockages in two general areas. These partial blockages are likely the result of solids settlement caused by velocities below those needed for self-cleaning. Current access from the shoreline for cleaning is limited, and settled solids cannot effectively be removed using the shore-based cleaning protocol. Therefore to address these partial blockages, it is proposed that three existing submerged manholes on the lake line be temporarily accessed for cleaning. Temporary access from the lake surface will be obtained with steel riser sections connected to the manhole structure. It is proposed that two additional submerged manholes be installed to increase the extent of the pipeline that can be cleaned. In addition to addressing partial pipe blockages, the proposed summer work will include condition assessment on parts of the pipe not currently exposed. This will enable additional analyses of the pipe material to determine the amount of corrosion and remaining useful life of the pipe to aid in the City’s strategic planning process. A permit application will be prepared with a description of the work and the locations where each task will be performed. Permitting figures are enclosed, which show the location of each type of work and detailed drawings of the manholes to be installed. Technical Memorandum Description of Proposed Summer 2018 Work/March 28, 2018 2 Description of Work Location of Work The location of work is shown in Figures 1 -3. Figure 4 lists properties where the work is proposed as well as adjacent properties that may experience temporary construction impacts. The community outreach database maintained by EnviroIssues for the Condition Assessment project was reviewed for the properties. Coordination with property owners is anticipated as part of the preparation for the work. However, no significant issues were identified based on recorded previous communications. Additional Manholes The two proposed manholes will be installed on the lake line sewer in front of the following properties.  2905 Mountain View Ave N; and  3115 Mountain View Ave N. The following properties adjacent to the manhole locations may experience short-term construction impacts.  2827 Mountain View Ave N;  2909 Mountain View Ave N;  3111 Mountain View Ave N; and  3119 Mountain View Ave N. The two proposed manholes will be at low points along the undulating sewer to facilitate solids removal. Their locations will facilitate cleaning of a partial blockage believed to be impacting the southern portion of the pipe. The existing manholes will be used to clean the northern blockage. The proposed manholes will be buried to comply with anticipated permit requirements. Flexible couplings will be installed on the lake line approximately 10 feet from the manhole, to enable localized lowering of the sewer profile and ensure that the manhole cover is below the lakebed. This will allow the manholes to be installed without permanently modifying the lakebed, which would trigger a more intensive permitting process and likely preclude this work from being performed during the 2018 fish window. Lake Line Cleaning Cleaning of the lake line will be performed from the two new and three existing submerged manholes on the sewer. They will be accessed via steel riser sections that can be connected to the top of the manholes. Once accessed, wastewater from the manholes and adjacent sections of the lake line will be removed prior to cleaning. It is proposed that cleaning will use a jetter hose to flush solids toward the manhole where they will be removed by a vacuum. Closed circuit television (CCTV) inspection will be performed before and after cleaning to evaluate the effectiveness of the cleaning procedure. All the work will be performed from work boats or a barge in Lake Washington. Pipeline Sampling for Condition Assessment Physical samples of the pipeline will be taken to assist with condition assessment of the lake line and laterals.  The lengths of sewer removed as part of manhole installation will be analyzed as part of the condition assessment. These will provide information on pipe condition along the southern part of the lake line.  One additional coupon will be collected near 3703 Lake Washington Blvd N along the northern part of the lake line. This coupon is at a relatively high elevation along the lake line more likely to have been exposed to corrosive atmosphere. This will aid in formulating a conservative estimate of the remaining useful life of the system. Technical Memorandum Description of Proposed Summer 2018 Work/March 28, 2018 3  Coupons will also be collected on laterals in front of 2905 Mountain View Ave N, 3107 Mountain View Ave N, and 3703 Lake Washington Blvd N. Pipeline sampling at these locations may also impact the adjacent properties at 2909 Mountain View Ave N and 3103 Mountain View Ave N. These laterals are at relatively high elevations along the lake line and experience intermittent gas exposure, and coupons will provide information about pipe corrosion under adverse conditions. Ultrasonic thickness testing is proposed at five points along the main line (3101 and 3213 Mountain View Ave N and 3307, 3401, and 3501 Lake Washington Blvd N). These are distributed along the length of the main line and include both high points and low points to assess pipe thickness under various conditions.